High Pressure Sodium to LED Conversion Calculator

High Pressure Sodium (HPS) Lamp Watts

What is the wattage of the current High Pressure Sodium light bulb you are using? Select it from the drop-down list provided.

System Watts

HPS light fixtures have a lamp (light bulb) and a ballast. The ballast converts the electrical voltage supplied to power that ignites and keeps the lamp on. System watts is the combined wattage of the lamp and the electricity used by the ballast. The most common answer is provided.

Lamp Mean Lumens

High Pressure Sodium lamps, like all lamps, suffer lumen deprecation. When a HPS lamp is new, the lamp emits more light than when the lamp is 40% or more through the lamp’s average life. Mean lumens is the recognized or design lumens emitted. It is the average lumens emitted by the lamp over the life of the lamp.

Scotopic/Photopic (S/P) Ratio

The scotopic/photopic ratio, or S/P ratio, is a ratio or multiplier that measures how much of the light emitted is useful or visible to the human eye. Useful lumens are known as visually effective lumens or VELs. A light source with a higher S/P ratio, like one using 5700K LEDs, will provide superior visibility including better color rendering. For more information on Scotopic/Photopic Ratios, click here,

Visual Equivalent Lumens (VELs)

Visually effective lumens or VELs are calculated by multiplying the lumens supplied by the light source times the appropriate S/P Ratio.

LED Replacement S/P Ratio

Every light source has a S/P ration even if the S/P Ratio is 1.00. This part of the calculation applies the S/P ratio to the new LED light source. Each LED Kelvin has a respective S/P Ratio. Select the Kelvin of your new LED light source and the calculator will use the correct S/P Ratio.

Luminaire Efficacy

HPS luminaires (light fixtures), have optics in the form of reflectors, refractors and/or lenses that enhance the light emitted from the lamp and aid in directing the light emitted from the lamp. While some optics try to increase the light emitted, most maintain or reduce the light emitted. Also, due to the luminaire design, some light may simply be blocked from getting out. Luminaire efficacy is a measure of the percentage of lamp lumens the are emitted from the luminaire. The luminaire efficacy default selection is 80%. If you want a more accurate luminaire efficacy percentage recommendation, speak with an Access Fixtures Lighting Specialist.

LED Fixture Lumens Per Watt

When purchasing a LED luminaire, LED Fixture Lumens per Watt information should be provided. The performance factors that you want are system watts and LED Fixture Lumens per Watt. System watts is the total wattage of the LEDs based on the mA provided by the LED driver and the wattage used by the LED driver. There is also a difference between LED lumens and luminaire lumens. LED lumens is the lumens per watt of the LEDs. Just like legacy luminaires, the lamp lumens are not the same as the luminaire lumens. Luminaire lumens is the lumens emitted by the LEDs installed in the luminaire. The information that you ultimately want is LED Fixture Lumens per Watt. That is LED Luminaire Lumens divided by LED System Watts. Again, this should be provided, but be sure that you are getting the correct information. It should be noted that LED Luminaire Lumens and consequently LED Luminaire Lumens per Watt will be lower when using lower Kelvin LEDs.

If you are planning on using a LED retrofit lamp in an existing fixture, the math may be somewhat different. If the luminaire has a lens, the efficacy of the LED retrofit efficacy will be significantly lowered. This is due to how LEDs lose efficacy when the light is transmitted through glass. For example, LED retrofit light loss of LED light transmitted through prismatic glass is approximately 30%. Speak with an Access Fixtures lighting specialist to know your options and to determine your best solution.

Equivalent with Maintenance Factor (MF)

Like legacy luminaires, LED luminaires have lumen depreciation too. While lumen loss is much less and takes place over a greater time, lumen loss must be taken into consideration to ensure sufficient light for the tasks to be performed. A calculation is required that is similar to HID Mean Lamp Lumens. LED luminaires have an L70 rating such as L70 @ 100,000 Hours. That means that over 100,000 hours of use the lumens emitted will decline to 70% of the original light emitted by the LED luminaire. While that is a long time, time passes. Enough light when new may not or will not be enough light later. Access Fixtures lighting engineers recommend that a MF of 20%. be added to maintain sufficient lumens for the task.